Semipermeable membranes from modified polymers

ABSTRACT

Polymers from the group consisting of cellulose and its ester and ether derivatives, of polyvinyl alcohol and its ester derivatives, copolymers with vinyl esters and homopolymers and copolymers of acrylates and methacrylates are modified with monofunctional or difunctional cyclic β-ketonic acids or their esters, in particular with succinylsuccinic acid or its ester derivatives. The modified polymers are particularly suitable for obtaining semi-permeable membranes for osmotic separation methods.

This is a divisional of application Ser. No. 13,501, filed on Feb. 21,1979, now U.S. Pat. No. 4,249,000, issued Feb. 3, 1981.

The present invention relates to polymers from the group consisting ofcellulose esters and ethers, of polyvinyl alcohol and the esterderivatives thereof, of copolymers with vinyl esters and of thehomopolymers and copolymers of acrylates and methacrylates which aremodified with cyclic β-ketonic acids or their esters, in particular withsuccinylsuccinic acid or its esters, a process for the manufacture ofsaid polymers and the use thereof for obtaining membranes for methods ofseparating substances, for example chromatography, electrodialysis and,in particular, hyperfiltration (reverse osmosis).

The utilisation of reverse osmosis for water treatment, for example fordesalinating sea water, purifying brackish water or purifyingwastewaters, has attained economic importance in recent years. Plasticmembranes, on whose mechanical strength, chemical resistance andseparating efficiency great demands are made, are used for suchtreatment methods. Membranes made of cellulose esters and polyamides arechiefly used. Such membranes still exhibit deficiencies as regards theirseparating efficiency and there is consequently a need for improvementin this respect. The biological degradation of the membranes is alsoobserved to be a substantial drawback, which becomes especially apparentin the loss of the mechanical strength.

The present invention has for its object the provision of modifiedpolymers which are suitable for methods of separating substances, inparticular for obtaining semi-permeable membranes for hyperfiltrationmethods, and which eliminate the deficiencies referred to above.

Accordingly, the present invention provides polymers from the groupconsisting of cellulose ester and ether derivatives, of polyvinylalcohol and the ester derivatives thereof, copolymers with vinyl estersand of the homopolymers and copolymers of acrylates and methacrylates,said polymers containing radicals of monofunctional or difunctionalcyclic β-ketonic acids or their esters which are bonded through estergroups. In the case of polymers which contain hydroxyl groups, theradicals are bonded direct through the carboxyl groups of the β-ketonicacids. In the case of polymers which contain carboxyl groups, theβ-ketonic acids are bonded through their acid group by means of divalenthydrocarbon radicals R of aliphatic, cycloaliphatic or aromaticcharacter according to the scheme

    --COO--R--OOC--polymer.

Examples of cyclic β-ketonic acids which are known per se are:1-carboxycyclopentan-2-one, 1,4-dicarboxycyclopentane-2,3-dione,1,3-dicarboxycyclopentane-2,3-dione,1,3-dicarboxycyclopentane-2,4-dione, 2,3-dicarboxycyclohexane-1,4-dione,3,5-dicarboxycyclohexane-2,6-dione, 1-carboxycyclohexan-2-one and, inparticular, 3,6-dicarboxycyclohexane-1,4-dione (succinylsuccinic acid).

Accordingly, especially preferred radicals of cyclic β-ketonic acids arethose of succinylsuccinic acid or its ester derivatives of the formula I##STR1## wherein R represents a divalent hydrocarbon radical ofaliphatic, cycloaliphatic or aromatic character and R' represents amonovalent hydrocarbon radical of aliphatic, cycloaliphatic or aromaticcharacter which is unsubstituted or substituted by hydroxyl, and x, inthe case of the cellulose derivatives and polyvinyl alcohols and theirderivatives, is 0, and, in the case of the acrylate and methacrylatehomopolymers and copolymers, is 1.

R in formula I as divalent hydrocarbon radical of aliphatic charactercan be linear or branched alkylene which is interrupted by oxygen andwhich preferably contains 2 to 12, in particular 2 to 6 and mostpreferably 2 or 4, carbon atoms. Examples are: ethylene, 1,2- or1,3-propylene, 1,2-, 1,3- or 1,4-butylene, pentylene, neopentylene,hexylene, octylene, dodecylene and, for example, the radicals of theformula --(C_(n) H_(2n) O)_(m) derived from polyoxaalcohols, wherein mis a value from 2 to 10 and n is an integer from preferably 2 to 4.Examples of these radicals are the radicals of diethylene, triethyleneor tetraethylene glycol, dipropylene glycol or dibutylene glycol.

R in formula I as divalent hydrocarbon radical of cycloaliphaticcharacter can be cycloalkylene, alkylenecycloalkyl andbisalkylenecycloalkyl. Examples are: cyclopentylene, cycloheptylene and,in particular, cyclohexylene. Further examples are methylenecyclohexyland 1,4-bis-methylenecyclohexane.

R in formula I can also be a divalent hydrocarbon radical of aromaticcharacter, in particular one of phenyl-aromatic character, for examplephenylene, benzylene and xylylene. Preferably, R in formula I isalkylene.

R' in formula I as monovalent hydrocarbon radical which is unsubstitutedor substituted by hydroxyl can contain 1 to 30, preferably 1 to 22, inparticular 1 to 12 and most preferably 1 to 6, carbon atoms, and bealkyl, hydroxyalkyl, cycloalkyl, aryl, alkaryl or aralkyl. The alkyl andhydroxyalkyl radicals are preferred. These can be linear or branched andcan contain preferably 1 to 12 and, in particular, 1 to 6, carbon atoms.Examples of R' are: methyl, ethyl, propyl, isopropyl, butyl, isobutyl,pentyl, hexyl, octyl, dodecyl, hexadecyl, octadecyl, eicosyl,β-hydroxyethyl, γ-hydroxypropyl, δ-hydroxybutyl, hydroxycyclohexyl,hydroxyphenyl, cyclopentyl, methylcyclohexyl, cyclohexyl, cycloheptyl,phenyl, naphthyl, benzyl, β-phenethyl, methylphenyl, butylphenyl,octylphenyl, nonylphenyl, methylbenzyl, octylbenzyl.

Preferred polymers are cellulose ester and cellulose ether derivatives,of which the ester derivatives are particularly preferred.

Ester and ether derivatives of cellulose are, for example,nitrocellulose, acetyl cellulose, cellulose triacetate, celluloseacetopropionate, cellulose acetobutyrate, cellulose tripropionate,cellulose tributyrate, cellulose benzoate, methyl cellulose, oxyethylcellulose, carboxymethyl cellulose, ethyl cellulose, benzyl cellulose.Cellulose acetate with a different degree of acetylation is preferred.

The cellulose polymers of the invention preferably contain in additionhydroxyl groups. This is particularly advantageous in the use of osmosismembranes.

A further suitable polymer is polyvinyl alcohol and its partially orcompletely esterified derivatives. Ester derivatives are in particularpolyvinyl acetate and polyvinyl propionate, but also those containingother acyl radicals, such as benzoyl, formyl, butyryl or stearyl.

A further group of polymers comprises the copolymers of vinyl esters(vinyl acylates) with one or more other comonomers. They can be blockcopolymers or statistical polymers. Examples of comonomers are:

α-olefins, such as ethylene, propylene, butylene, isobutylene,methylbutene-1, methylpentene-1 and butadiene, isoprene, styrene,acrylonitrile, methacrylate, methylmethacrylate, ethyl acrylate, butylacrylate, vinyl chloride, vinylidene chloride, acrylamide, dimethylbutadiene, chloroprene, methylstyrene, vinyl carbazole, vinyl fluoride,acrylic acid.

Examples of copolymers are: ethylene/vinyl acetate, vinyl chloride/vinylacetate, propylene/vinyl acetate, vinyl acetate with other vinyl estersor acrylic esters, for example acrylic acid ester, fumaric acid ester,maleic acid ester, vinyl laurate, vinyl stearate.

A further group comprises the homopolymers of acrylic acid, methacrylicacid and, in particular, the esters thereof with, for example, methanol,ethanol, propanol, butanol, dodecanol. To this group also belong thecopolymers with, for example, one or more of the above mentionedcopolymers. Examples are: polymethacrylate, polymethylmethacrylate,polyethylacrylate or polyethylmethacrylate, polybutylacrylate,copolymers of methylacrylate or ethylacrylate or methylmethacrylate orethylmethacrylate with acrylonitrile, styrene, vinyl chloride,butadiene, such as acrylonitrile/methacrylate,acrylonitrile/methylmethacrylate, acrylonitrile/styrene/methacrylate,styrene/acrylic acid, methacrylate/butadiene/styrene, ethylene/acrylicacid, ethylene/ethylacrylate.

The average number of radicals of the formula I bonded to the polymerside chains and contained in the cellulose polymers and theirderivatives is, per monomer unit, up to 1, preferably 0.01 to 1, inparticular 0.05 to 0.8 and, most preferably, 0.1 to 0.5.

The average number of radicals of the formula I bonded to the polymerside chains and contained in the vinyl alcohol, vinyl ester, acrylateand methacrylate polymers and copolymers is, per functional monomerunit, up to 1, preferably 0.01 to 1, in particular 0.05 to 0.9, and,most preferably, 0.1 to 0.5. It has been found that the desiredmodification is effected with a relatively small content of radicals ofcyclic β-ketonic acids.

The preferred thermoplastic polymers of the invention are obtained bytransesterifying or esterifying cellulose esterification derivatives oretherification derivatives containing hydroxyl groups, polyvinylalcohol, the ester derivatives thereof, copolymers with vinyl esters orhomopolymers or copolymers of acrylates or methacrylates in the meltphase or preferably solutions of the polymers, in an inert solvent, withmonofunctional or difunctional cyclic β-ketonic acids or esters.

The polymers used as starting materials are for the most partcommercially available or they can be easily prepared by knownpolymerisation methods.

The cyclic β-ketonic acids and their esters are known. Thesuccinylsuccinates are also commercially available products or they canbe easily prepared. They are also described in the literature (cf. forexample H. Holtschmidt, Makromol. Chemie 13, 1954, page 141 ff.).

Depending on the starting polymers, two different types of ester groupbonding are obtained, which bond the radicals of the cyclic β-ketonicacids to the polymer chains:

(1) If hydroxylated polymers (cellulose derivatives, polyvinyl alcohol)or their esterification derivatives are used, products are obtained inwhich radicals of the formula I are bonded to the polymer chains throughoxygen atoms of the carboxyl group of the β-ketonic acids (x in formulaI is 0).

(2) If starting polymers containing carboxyl or carboxylate side groups(acrylates and methacrylates) are used, polymers are obtained in whichradicals of the β-ketonic acids are bonded to these carboxylate sidegroups through divalent hydrocarbon radicals (x in formula I is 1).

Accordingly, it is possible in (1) for example to usesuccinylsuccinates, including the ester derivatives which containhydroxyl groups. Preferably, lower alkyl esters are used. In (2), it isonly possible to use succinylsuccinates of the formula I, wherein one R'or both R' represent a hydrocarbon radical of aliphatic, cycloaliphaticor aromatic character which is substituted by hydroxyl. Especially inthis case, R' is alkylene of preferably 2 to 6 carbon atoms.

In (1), reaction temperatures of preferably at least 120° C., inparticular 120° to about 180° C., are used, and in (2), the reactiontemperatures are from 0° C. to about 120° C., in particular from 50° to120° C.

In the process in the melt phase, the temperature depends on the meltingrange of the polymer. Advantageously, the temperature in this process isup to about 100° C., preferably not more than 50° C., above the meltingpoint of the polymer.

The catalysts conventionally employed in transesterification andesterification reactions can be used for the process, for exampleamines, inorganic or organic acids, for example hydrochloric acid orp-toluenesulfonic acid, or else metals or metal compounds, such as theoxides and salts or organic compounds of calcium, magnesium, zinc,cadmium, mangenese, titanium, tin and cobalt.

The water of reaction formed during the esterification, or the alcoholsand carboxylic acid esters formed during the transesterification, can beremoved from the reaction mixture during or after the reaction, forexample by azeotropic or simple distillation.

Suitable inert solvents for the process are aprotic, preferably polar,solvents, such as sulfones (tetramethylsulfone), sulfoxides (dimethylsulfoxide), ketones (cyclohexanone), acid amides (dimethyl formamide),ethers (tetrahydrofurane, dioxane), and halogenated hydrocarbons(methylene chloride, chloroform, carbon tetrachloride,tetrachloroethane).

The desired modified polymers are obtained direct in the melt phaseprocess. If the process is carried out in the presence of solvents, itis expedient to isolate the modified polymers by precipitating them fromthe reaction solutions, for example by cooling or by addition ofnon-solvents. Advantageously, they dissolve simultaneously non-reactedstarting material. For example, alcohols, such as methanol or ethanol,can be used for this purpose.

The preferably thermoplastic polymers of the invention can have lower orhigher viscosities than the starting polymers. The ketonic acids usedfor the modification also contain two functional groups, so that acrosslinking of the polymer chain can be expected to a small extentduring the reaction. Their mechanical properties are only changed to asmall degree. They are suitable thermoplastic polymers for themanufacture of mouldings by the conventional methods. On account of themodification, the polymers contain metal chelate-forming groups. Byimmersing the mouldings in metal salt solutions, it is possible toobtain an antistatic finish on the surface as a result of metal complexformation. The biological degradability (for example by bacteria orother microorganisms) can be effectively inhibited by the choice ofspecific heavy metal salts, such as cadmium, copper, mercury, iron,nickel or cobalt.

The combination of the properties of the polymers of the presentinvention for obtaining semi-permeable membranes for use in osmosis orreverse osmosis, is particularly advantageous. The good mechanicalproperties are retained over a prolonged period of time, as thebiological degradation can be inhibited. The ability of the polymers toform metal complexes makes it possible to obtain a stationary surfacepolarisation on the membranes. The particular advantage of thispolarisation is an increase in the separating efficiency of themembranes in reverse osmosis. An adjustment to the particular separatingproblem can be made as a result of the subsequent production of thesurface polarisation. The desired polarisation can also be effecteddirect during the reverse osmosis by dissolved metal salts. A betterretention of the metal salts dissolved in the water to be purified issubstantially achieved with the polarisation. In addition, increasedhydrophilic properties are observed, which in turn make possible anincrease in the rates of flow. It is especially advantageous that theloss of mechanical properties connected with the high water absorptioncan be compensated for by a chelation with metal ions. The polymers ofthe present invention can also be used in liquid chromatography andelectrophoretic methods.

The semi-permeable membranes can be asymmetrical or in the form of athin layer. The thickness of the active layer is in general 0.05 to0.2μ, preferably 0.1 to 0.15μ. The thickness of the asymmetricalmembranes can be from 0.1 mm to 5 mm.

The following Examples illustrate the invention in more detail.

EXAMPLE 1

Acetyl cellulose (39.8% acetyl content, 17.3 g) is dissolved in dimethylsulfoxide (60 ml) and heated to 150°-160° C. Strongly acidicion-exchange resin (0.5 g) and diethyl succinyl succinate (50 g) areadded. The reaction mixture is subsequently stirred for 2 hours at170°-175° C. After cooling, methylene chloride (100 ml) is added and theresulting solution is poured into methanol (1500 ml). The product isprecipitated and the precipitate is recrystallised twice and driedovernight at 70° C./0.1 mm, affording 14.8 g of modified celluloseacetate of relative viscosity 2.34. It has a UV absorption (intetrahydrofurane) of max.=246 mm. It was not possible to detect freediethyl succinylsuccinate (max.=242 mm). A solution of the modifiedpolymer (2.9 g in 1000 ml of tetrahydrofurane) has an extinctionE=0.367. From this value it can be calculated that the averagesubstitution of the monomer units is 5.5.

EXAMPLE 2

42.4 g of di-(β-hydroxyethyl)-succinyl succinate are heated to 165° C.and 15 g of powdered polymethylmethacrylate are added. The mixture issubsequently kept for 1 hour at 170° C. and then cooled. The reactionmixture is then taken up in 100 ml of methylene chloride and the productis precipitated with 1.5 liters of methanol. The precipitate isisolated, dissolved in 200 ml of methylene chloride and freed frominsoluble constituents by centrifuging. A further precipitation with 1liter of methanol yields, after drying in vacuo, 4 g of modifiedpolymethylmethacrylate having a UV absorption band of λmax.=242 mm. TheNMR spectrum shows a 14% content of succinyl succinate radicals,corresponding to an average of about 1 radical per 7 monomer units.

EXAMPLE 3 (USE EXAMPLE)

2 g of modified cellulose acetate containing on average 1 ethylsuccinylsuccinate per 8 monomer units is prepared in accordance with theparticulars of Example 1, powdered, and stirred for 1 hour in asaturated aqueous copper acetate solution. The modified cellulosetriacetate is then isolated and initially washed with water. The coppercontent is determined by washing 3 times with 0.1 N hydrochloric acidand then with water. 15.8 mg of copper are detected in the washings.Repetition of the procedure with the same sample shows an increase of13.4 mg of copper, and a further repetition shows an increase of 12 mgof copper.

By comparison, an unmodified sample of cellulose triacetate (2 g) showsan increase of only 1.6 mg, 1.2 mg and 1.1 mg of copper under the sameconditions.

EXAMPLE 4 (USE EXAMPLE)

Test of the biological activity of modified acetyl cellulose films. 1cm² of each of the following films:

I. cellulose acetate (comparison)

II. cellulose acetate of Example 3 modified with diethylsuccinylsuccinate (comparison)

III. cellulose acetate treated with copper acetate (comparison)

IV. II treated with copper acetate (according to the invention) isplaced either on Caso agar which has been inoculated with Streptomycescellulosum using a spatula, or on malt extract agar on which fungusspores of Chaetum globosum have been spread with a spatula. The platesare incubated for 7 days at 28° C. Evaluation was made in accordancewith the following rating:

1=film attacked by micro-organisms

2=film attacked to an insignificant extent by micro-organisms

3=film not attacked by micro-organisms

4=film not attacked by micro-organisms+inhibiting aerole

For control purposes, the films are placed on non-infected Caso agar andmalt extract agar.

The results are reported in the following table:

    ______________________________________                                        Strain      Agar       Cellulose sheet                                                                             Rating                                   ______________________________________                                        control 1                                                                     --                        I          1                                        --          malt          II         1                                        --          extract       III        1                                        --                        IV         3                                                                  I          1                                        Chaetomium  malt          II         1                                        globosum    extract       III        1                                                                  IV         2-3                                      control 1                                                                     --                        I          1                                        --          Caso          II         1                                        --          agar          III        1                                        --                        IV         3                                                                  I          1-2                                      Streptom    Caso          II         1-2                                      cellulosum  agar          III        1                                                                  IV          4*                                      ______________________________________                                         *strain inhibited on the entire surface.                                      1 The films were already infected from the start by microorganisms which      were able to replicate thereon.                                          

Only the modified cellulose film treated with Cu²⁺ ions exhibited no oronly very insignificant attack by the foreign-body infections and byChaetum globosum and Streptomyces cellulosum.

The cellulose films can be effectively protected from microbiologicalattack and consequent degradation by the modification and treatment withCu ions. The modification alone does not afford protection fromdegradation.

EXAMPLE 5

An approx. 0.3 to 0.6 mm film of modified acetyl cellulose (acetylcontent 37.2%, modified with 20 mol.% of β-hydroxyethylsuccinylsuccinate) is immersed overnight in water. In this state, the film had atensile strength of 1.6 N/mm². The film is then immersed for 4 hours inan aqueous nickel acetate solution and the tensile strength isafterwards determined again. It is now 2.9 N/mm². By comparison, thevalues obtained for an unmodified sheet subjected to treatment under thesame conditions are 3.31 and 3.73 N/mm².

A substantially lower increase in the tensile strength of the unmodifiedsheet is obtained. The modification is allied to an increase in thehydrophilic properties, which diminish the mechanical properties.Surprisingly, however, the diminishment of the mechanical properties canbe very largely compensated for by the treatment with salt solutions,especially of transition metals, whereby the field of use is virtuallynot impaired.

EXAMPLE 6

A modified cellulose acetate film prepared according to Example 1 andcontaining one cellulose unit substituted with diethylsuccinyl succinateper 3 cellulose units, is dissolved in a mixture of acetone/formamideand an approx. 0.4 mm asymmetric film is cast from the solution. Anasymmetric film is likewise prepared from the basic cellulose acetate.

The flux F and ion retention capacity R and the changes allied to thecontact of the salt solution with the membrane are determined with thesefilms in successive steps, without changing the films, at a pressure of40 and 60 bar and a pH value of about 3.7 using 0.1 N NaCl and CuCl₂solutions. For comparison purposes, the rate of flow of pure water issimultaneously determined.

The flux is indicated in 1/m² d and the ion retention capacity in %. Theselectivity T Cu/Na (M) is the quotient of the copper and sodiumretention.

The membranes are tested with the solutions in the following sequenceand the indicated values determined:

(a) water (F H₂ O)

(b) 0.1 N NaCl solution F NaCl(I), RNa (I), R Cl(I)

(c) 0.1 N CuCl₂ solution F CuCl₂ (I), R Cu(I), R Cl(I)

(d) 0.1 N NaCl solution F NaCl(II), R Na(II), R Cl(II)

(e) 0.1 N CuCl₂ solution F CuCl₂ (II), R Cu(II), R Cl(II)

(f) 0.1 N NaCl/0.1 N CuCl₂ solution F (M), R Na(M), R Cl(M)

The results are reported in the following table.

                  TABLE                                                           ______________________________________                                                 Film (invention)                                                                           Unmodified film                                         Properties                                                                              40 bar    60 bar    40 bar  60 bar                                  ______________________________________                                        F H.sub.2 O                                                                             748       2206      1122    7480                                    F NaCl (I)                                                                              1153      2244      374     1496                                    F CuCl.sub.2 (I)                                                                        1122      2742      374     2057                                    F NaCl (II)                                                                             1421      2618      374     2805                                    F CuCl.sub.2 (II)                                                                       1090      2306      598     1122                                    F (M)     935       2306      561     997                                     R Na (I)  31        31        83      37                                      R Cl (I)  27        29        79      29                                      R Cu (I)  52        37        82      46                                      R Cl (I)  34        12        84      48                                      R Na (II) 35        22        81      24                                      R Cl (II) 27        15        78      17                                      R Cu (II) 58        21        87      80                                      R Cl (II) 44        --        87      77                                      R Na (M)  29        4         82      57                                      R Cu (M)  50        15        88      60                                      R Cl (M)  36.5      12        83      54                                      T Cu/Na (M)                                                                             1.72      3.75      1.07    1.05                                    ______________________________________                                    

It is evident from the table that the rates of flow are substantiallyincreased by the modified film in contact with salt-containing solutionsand that the amount of waste is not as great as in the case ofcorresponding but modified films. A further increase can be attained bythe treatment with Cu-solution [comparisons of F NaCl (I) and F NaCl(II)]. By means of the same treatment, an increase of the salt retentionwith respect to the cations is also obtained at lower pressure. Theincrease in selectivity is observed from a comparison of the separatingfactors [T Cu/Na (M)].

What is claimed is:
 1. A semipermeable membrane prepared from a polymerselected from the group consisting of cellulose ester and celluloseether derivatives, polyvinyl alcohol and ester derivatives thereof,copolymers of polyvinyl alcohol and vinyl esters, copolymers of vinylesters with one or more α-olefin comonomers, and homopolymers andcopolymers of acrylates and methacrylates, said polymer containingradicals of a cyclic monofunctional or difunctional β-ketonic acid orits esters which are bonded through ester groups.
 2. A semipermeablemembrane according to claim 1 wherein the polymer is selected from thegroup consisting of cellulose ester and cellulose ether derivatives. 3.A semipermeable membrane according to claim 2 wherein the celluloseester or cellulose ether derivative additionally contains free hydroxylgroups.
 4. A semipermeable membrane according to claim 1 wherein theradicals are derived from a cyclic β-ketonic acid selected from thegroup consisting of 1-carboxycyclopentan-2-one,1,4-dicarboxycyclopentan-2,3-dione, 1,3-dicarboxycyclopentan-2,3-dione,1,3-dicarboxycyclopentan-2,4-dione, 2,3-dicarboxycyclohexan-1,4-dione,3,5-dicarboxycyclohexan-2,6-dione, 1-carboxycyclohexan-2-one or3,6-dicarboxycyclohexane-1,4-dione.
 5. A semipermeable membraneaccording to claim 1 wherein the radicals of the cyclic β-ketonic acidare radicals of 3,6-dicarboxycyclohexan-1,4-dione or its esterderivatives of the formula ##STR2## wherein R represents alkylene,cycloalkylene, benzylene, xylylene, phenylene orcyclohexane-1,4-dimethylene, R' represents alkyl, hydroxyalkyl,cycloalkyl, aryl, alkaryl or aralkyl; and x in the case of cellulosederivatives, polyvinyl alcohol or derivatives is 0, and, in the case ofacrylate or methacrylate homopolymers or copolymers is 1; and whereinthe average number of radicals of the cyclic β-ketonic acid or its esterderivatives that is bonded to the cellulose polymer is up to 1 radicalper cellulose monomer unit; or that is bonded to the vinyl alcohol,vinyl ester, acrylate or methacrylate homopolymer or copolymer is up to1 radical per functional monomer unit.
 6. A semipermeable membraneaccording to claim 5 wherein R is linear or branched alkylene of 2 to 12carbon atoms, or is cycloalkylene of 5 to 7 carbon atoms.
 7. Asemipermeable membrane according to claim 6 wherein R is alkylene of 2to 6 carbon atoms.
 8. A semipermeable membrane according to claim 7wherein R is alkylene of 2 to 4 carbon atoms.
 9. A semipermeablemembrane according to claim 5 wherein the average number of radicals ofthe cyclic β-ketonic acid or its ester derivatives bonded to thecellulose polymer is from 0.01 to 1 radical per cellulose monomer unit.10. A semipermeable membrane according to claim 9 wherein the averagenumber of radicals of the cyclic β-ketonic acid or its ester derivativesbonded to the cellulose polymer is from 0.05 to 0.8 radical percellulose monomer unit.
 11. A semipermeable membrane according to claim10 wherein the average number of radicals of the cyclic β-ketonic acidor its ester derivatives bonded to the cellulose polymer is from 0.1 to0.5 radical per cellulose monomer unit.
 12. A semipermeable membraneaccording to claim 5 wherein the average number of radicals of thecyclic β-ketonic acid or its ester derivatives bonded to the vinylalcohol, vinyl ester, acrylate or methacrylate homopolymer or copolymeris from 0.01 to 1 radical per functional monomer unit.
 13. Asemipermeable membrane according to claim 12 wherein the average numberof radicals of the cyclic β-ketonic acid or its ester derivatives bondedto the vinyl alcohol, vinyl ester, acrylate or methacrylate homopolymeror copolymer is from 0.05 to 0.9 radical per functional monomer unit.14. A semipermeable membrane according to claim 13 wherein the averagenumber of radicals of the cyclic β-ketonic acid or its ester derivativesbonded to the vinyl alcohol, vinyl ester, acrylate or methacrylatehomopolymer or copolymer is from 0.1 to 0.5 radical per functionalmonomer unit.
 15. A semipermeable membrane according to claim 1 whereinthe polymer is selected from the group consisting of the homopolymersand copolymers of acrylates and methacrylates.